LT6604-2.5
9
660425fa
–
+
1580Ω
0.01μF
0.1μF
3.3V
–
+
VIN
–
VIN
+
660425 F01
VOUT
+
VOUT
–
V
t
3
2
1
VIN
+
VIN
–
V
t
3
2
1
VOUT
+
1/2
LT6604-2.5
VOUT
–
0
25
27
4
34
6
2
29
7
–
+
1580Ω
0.01μF
0.1μF
3.3V
–
+
VIN
+
660425 F02
VOUT
+
VOUT
–
V
3
2
1
t
0
VOUT
+
VOUT
–
2
V
t
1
0
–1
VIN
+
25
27
4
34
6
2
29
7
1/2
LT6604-2.5
–
+
402Ω
0.1μF
0.01μF
5V
–
+
VIN
–
VIN
+
25
27
4
34
6
2
29
7
660425 F03
VOUT
+
VOUT
–
+
– 2V
V
t
3
2
1
0
VOUT
+
VOUT
–
V
t
3
2
1
0
VIN
+
VIN
–
500mVP-P (DIFF)
1/2
LT6604-2.5
APPLICATIONS INFORMATION
Figure 1
Figure 2
Figure 3
Interfacing to the LT6604-2.5
Note: The LT6604-2.5 contains two identical lowpass
lters. The following applications information only refers
to one lter. The two lters are independent except that
they share the same negative supply voltage V–. The two
lters can be used simultaneously by replicating the ex-
ample circuits. The referenced pin numbers correspond
to the A channel lter.
Each LT6604-2.5 channel requires two equal external re-
sistors, RIN, to set the differential gain to 1580Ω/RIN. The
inputs to the lter are the voltages VIN+ and VIN– presented
to these external components, Figure 1. The difference
between VIN+ and VIN– is the differential input voltage. The
average of VIN+andVIN–isthecommonmodeinputvoltage.
Similarly, the voltages VOUT+ and VOUT– appearing at pins
27 and 29 of the LT6604-2.5 are the lter outputs. The dif-
ference between VOUT+ and VOUT– is the differential output
voltage. The average of VOUT+ and VOUT– is the common
mode output voltage. Figure 1 illustrates the LT6604-2.5
operating with a single 3.3V supply and unity passband
gain; the input signal is DC-coupled. The common mode
input voltage is 0.5V, and the differential input voltage is
2VP-P. The common mode output voltage is 1.65V, and the
differential output voltage is 2VP-P for frequencies below
2.5MHz. The common mode output voltage is determined
by the voltage at VOCM. Since VOCM is shorted to VMID,
the output common mode is the mid-supply voltage. In
addition, the common mode input voltage can be equal
to the mid-supply voltage of VMID.
Figure 2 shows how to AC couple signals into the LT6604-
2.5. In this instance, the input is a single-ended signal.
AC-coupling allows the processing of single-ended or
differential signals with arbitrary common mode levels.
The 0.1μF coupling capacitor and the 1580Ω gain setting
resistor form a high pass lter, attenuating signals below
1kHz. Larger values of coupling capacitors will proportion-
ally reduce this highpass 3dB frequency.
In Figure 3 the LT6604-2.5 channel is providing 12dB of
gain. The common mode output voltage is set to 2V.